Locking fasteners and locking fastener assemblies are used to prevent loosening of a threaded fastener in a fastener joint. There are many types of threaded joints in which loosening of a fastener is undesirable. One example to which the principles of the present invention may be applied is an axle assembly of an automotive vehicle.
In a typical axle assembly, axle bearings are supported between an axle or spindle and a wheel hub or spindle support to permit rotation of a vehicle wheel. An axle bearing nut is used to hold the components together. In order to prevent premature bearing failure, the nut must be installed properly to avoid excessive axial bearing load or, alternatively, excessive free play. In addition, after assembly it is important to prevent loosening of the axle bearing nut to avoid bearing failure or even dangerous loss of a wheel.
A conventional axle assembly includes a spindle with male threads having an axially extending slot. A washer received on the spindle has a tab in the slot to prevent rotation of the washer. After the nut is threaded onto the spindle and tightened to the desired degree, part of the washer is deformed to lock the washer to the nut and prevent further rotation of the nut.
This conventional approach has disadvantages. One serious problem, especially in original mass production, is that installation of the washer and nut requires too many manual assembly steps. Another disadvantage is that the washer must be deformed both after installation of the nut and again when it is desired to remove the nut. The fact that the nut and washer are separate pieces makes it possible for the assembly to be installed improperly, for example without the washer or with an incorrect or damaged washer. Moreover, the locking of the nut against rotation is not as positive as desired because the washer can be deformed or broken.
In order to overcome such disadvantages of the conventional assembly, it has been proposed to provide locking fastener assemblies in which a washer and a nut are normally locked against rotation and in which the installation tool or wrench can be manipulated to free the nut for rotation. Examples of such proposals can be found in U.S. Pat. Nos. 3,851,690 and 3,942,570. While the assemblies disclosed in these patents overcome some disadvantages of the conventional nut and washer, they are subject in turn to other disadvantages. They include relatively delicate mechanisms requiring complex movements and are not well suited to the types of forces and environments encountered by automotive vehicles. In addition, they require special manipulation of an installation tool or wrench over and above the normal use of a wrench with a nut.
Another prior approach has been to use a nut and a non-rotating retainer normally separated by a spring and having interfacing teeth or similar locking structures. As the assembly is tightened, the spring force is overcome and the nut becomes locked to the retainer to prevent further rotation. In addition to complexity and expense, the arrangement has the disadvantage that as the nut reaches its final position, it is not free spinning. The ragged, uneven torque characteristic interferes with the use of torque detecting equipment that could otherwise detect a predetermined degree of tightening of the fastener assembly. Also, this assembly requires at least the amount of preload necessary to compress the spring normally separating the nut from the retainer.